The present invention relates to coextruded elastomeric breathable films for use in conformable garments and personal care products. More particularly, the present invention relates to multilayered films and film laminates for use with fabrics in disposable garments and personal care products.
The present invention is directed to thin multilayer films and their use in laminates and articles made therefrom. Film laminates have become an important article of commerce, finding a wide variety of applications, including use within various articles; for example, as outer covers for personal care products such as diapers, training pants, incontinence garments, feminine hygiene products and the like. In addition, film laminates have found use in various other bodily articles such as garments, surgical gowns, protective workwear, wound dressings, bandages and the like. The film can provide the desired barrier properties to the article while other materials laminated thereto can provide additional desired characteristics, such as abrasion resistance and/or good hand. In addition, in order to increase the comfort of the wearer, film laminates have been desirably xe2x80x9cbreathablexe2x80x9d, in the sense that the laminates act as a barrier to liquids, but allow water vapor and air to pass therethrough. By achieving and maintaining high breathability, it is possible to provide an article that is more comfortable to wear since the migration of water vapor through the fabric helps reduce and/or limit discomfort from excess moisture trapped against the skin. Thus, such an article can potentially contribute to an overall improved skin wellness. Therefore, it is often desirable to use a film to achieve desired comfort levels in an article. To this end, films have been engineered to achieve specific desired objectives.
For instance, while a variety of film laminates are known in the art, one particularly useful laminate uses a breathable barrier comprising a stretched filled multilayered (as opposed to a monolayer) microporous film. Such films are typically comprised of a relatively thick and often more expensive core layer, encompassing the majority of the film material, and relatively thinner outer skin layers. The core layer is often filled with particles or other matter and then crushed or stretched to form a fine pore network throughout the layer. The pores result from the separation of the polymer from the filler particles. The film-pore network allows relatively high levels of gas and water vapor to pass through the film while acting as a barrier to liquids and particulate matter. The amount of filler within the film and the degree of stretching is controlled so as to create a network of micropores of a size and/or frequency to impart the desired level of breathability to the fabric.
An exemplary stretched filled-film is described in commonly assigned WO Patent Application 96/19346 to McCormack which discloses a multilayered filled-film comprising a breathable microporous core layer made from an extrudable thermoplastic polymer such as a polyolefin, including copolymers and/or blends thereof. One or more breathable microporous skin layers are attached to the core layer. McCormack emphasizes use of a generic type core layer and specifically designed skin layers. The described skin layers include extrudable thermoplastic polymers and/or additives designed to impart specialized properties to the overall film. The selection of skin layer polymers in the McCormack reference depends on the overall film attributes desired. Possible skin layer polymers are described, including homopolymers, copolymers and blends of polyolefins as well as ethylene vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene acrylic acid (EAA), ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), polyester (PET), nylon, ethylene vinyl alcohol (EVOH), polystyrene, polyurethane and olefinic thermoplastic elastomers. Additionally, McCormack describes the use of anti-block material to improve processing and/or to prevent unwanted adhesion of layers. The particulate filled-film of McCormack can be stretched to impart breathability. The stretched film may then be laminated to a nonwoven web to create a laminate that takes advantage of the strength and integrity of the nonwoven web and the barrier properties of the stretched film. The McCormack reference does not provide for the use of higher performance elastomers, while still providing a relatively high level of breathability at low cost.
Films have also been designed with skin layers that specifically help to reduce the occurrence of die lip buildup, that is the residual buildup of filler particles which tend to accumulate on an extruder die as the filled polymer is extruded during the film manufacturing process. This buildup of material on the die lip slows the manufacturing process since it requires the process to be stopped in order for the die lip to be scraped clean of the excess material. Such skin layers including EVA, are often used in order to reduce this accumulation of the filler particles.
Commonly assigned WO Patent Application 99/14262 to Shawver et al. describes a breathable microporous film comprised of a thermoplastic polymer blend of a first polyethylene polymer having a density below 0.89 g/cm3, a second polyethylene polymer having a density above about 0.90 g/cm3, and a filler. In particular, the reference describes the use of a single site/metallocene catalyzed polyethylene as a film component. While the attributes of this film are described as providing good breathability and body conformance, as well as not suffering from shrinkage when exposed to heat, the Shawver reference does not describe strategically placed higher cost elastomeric materials to help buttress the elastomeric properties of lower cost elastomers in a film, nor the use of higher performance elastomers while still achieving relatively high levels of breathability. Although such films demonstrate elastic properties, a film having better elastic properties than that of metallocene catalyzed polyethylene elastomers is desirable.
In addition to breathability of the multilayered film laminate, the ability of the laminate to exhibit higher performance elastic properties allows a garment made therefrom to provide better body conformance. However, providing a low cost multilayered laminate that achieves the desired conformance and breathability is problematic, particularly with stretched filled-films. In order to achieve good body conformance, the polymer composition of the film layers desirably should have good stretch and recovery properties and yet must also be capable of allowing formation and retention of pores upon processing. These two objectives are often at odds with each other.
For instance, U.S. Pat. No. 5,691,034 to Krueger et al. describes a multilayered elastomeric laminate with microtextured skin layers. The multilayered laminate is comprised of at least one elastomeric layer and at least one thin skin layer prepared by coextrusion. The laminate is illustrated in the patent as having three layers. Following coextrusion, the laminate is stretched past the elastic limit of the skin layers and allowed to recover. While the Krueger reference provides for the use of costly high performance elastomeric materials, it does not provide for breathability in the described laminate. This is particularly difficult to achieve using higher performance elastomers since these elastomers also lead to pore closure following stretching. Essentially, because of the retraction properties of the elastomer materials, the micropores necessary to make the film breathable do not always remain open after the stretching process.
One solution to this problem has been to add additional filler to reduce the tendency for the material to retract, thus allowing more micropores to remain open, thereby producing a breathable product. However, this decrease in the retraction attribute produces a higher percent set in the final product, that is generally a percent of elongation following stretch, resulting in a loss of fit or sagging over time when used in an article that will encounter movement (also known as dampening).
It is also known to use five layers in a multilayered film to achieve a breathable film. Such films often require tie or adhesive layers to bind the various skin/outer layers to a central core layer. It has been found that the use of an adhesive component in the core layer leads to manufacturing difficulties as the tackifier often promotes unwanted sticking/adhesion during the film manufacturing process. A five layered film structure is disclosed in U.S. Pat. No. 5,164,258 to Shida et al. Shida discloses a multilayered structure having a monolithic film core layer of a hygroscopic gas barrier and inner and outer surface layers engineered to facilitate the escape of moisture which becomes absorbed in the core. The outer layers are described as either foamed or filled, in order to increase their water vapor transmission rate (WVTR). Shida et al. does not describe elastic attributes of the multilayered films.
Furthermore, three and five layer films are described in commonly assigned WO Patent Application 97/04955 to Forte. Forte describes a multilayered breathable film and a method for making such a film. The five layered film, which is preferred over a described three layer embodiment, includes two adhesive, microporous layers to facilitate bonding of the various layers. The outer layers are monolithic and the microporous core layer is filled to achieve a desired level of breathability, or WVTR. In describing five layer films having adhesive layers, the Forte reference discloses a core layer that includes a thermoplastic polymer containing a metallocene catalyzed polyethylene. Forte also describes the outer monolithic skin layers as comprising a hydrophilic polymeric resin. In particular, Forte describes the use of certain resins, and in particular Pebax(copyright) brand polymeric resins in the outer five layers, specifically Pebax(copyright)4033 resin.
The three layered films described in the Forte reference utilize a microporous and adhesive core layer, with the adhesive component comprised of either polymeric materials capable of bonding to the layers, a mixture of materials from the outer monolithic layer, or scraps of multilayered films. The three layered embodiment described in this patent does not include a separate outer adhesive layer but makes use of an EMA material melt blended in the noncompatible skin layer to promote compatibility between the skin and core layer materials.
While Forte describes microporous multilayered films which are elastomeric, Forte does not describe a multilayered film which strategically places higher performance elastomeric materials in various positions in the film composite in order to buttress lower performance, lower cost elastomeric materials, and which are particularly effective at a certain stretch, and also does not describe xe2x80x9cproductxe2x80x9d films of relatively high breathability, which are themselves capable of specific additional stretch and recovery attributes, especially for the three layered film embodiment.
Thus, there exists a need for an efficient film and laminate thereof which is capable of providing relatively high breathability (i.e. WVTR) and body conformance, with the use of mainly lower cost elastomers, but including higher cost, high performance elastomers strategically placed in a film composite to buttress the performance of the relatively low performance elastomers, and without sacrificing breathability. There exists a need for a product multilayer film and film laminate which themselves demonstrate the attributes of stretch with significant recovery or retraction. Such an improvement would benefit the maintenance of fit of an article produced from such films and/or laminates. There exists a need for a multilayered elastic and breathable film with reduced die lip buildup during manufacture and which includes a compatibilizer to allow for the coextrusion of both polar and non-polar materials. Further there exists a need for a three layered film which is both elastic and breathable and yet does not suffer from the logistical complications of manufacturing a five layered film.
The aforesaid needs are fulfilled and the problems experienced by those skilled in the art overcome by the multilayered film of the present invention, which includes a filled core layer of a first elastomer, a primarily relatively low cost, low performance elastomer, and at least one monolithic skin layer of a second elastomer, a higher performance elastomer to help buttress the elastomeric attributes of the core layer. The filled-film is stretched/oriented to create a microporous film having voids adjacent to the filler wherein the film has a WVTR of at least 1,000 g/m2/24 hours. The resulting microporous film of the present invention demonstrates elasticity without sacrificing breathability. Desirably, the core layer is comprised of a less costly, low performance elastomer having a hysteresis value greater than about 75 percent such as a polyolefin elastomer, and in particular elastomeric metallocene-catalyzed polyethylene. Alternatively, small amounts of higher performance elastomer, such as a styrenic block copolymer (such as a Kraton(copyright) G) may be blended with the lower performance-lower cost elastomer in the core to improve the overall elastic performance of the material.
Desirably, the skin layers are comprised of blended higher performance elastomers, and in particular thermoplastic polyurethane elastomers and polyetheramides having a hysteresis value of less than about 75 percent and desirably less than 60 percent. Desirably, EMA with high methyl acrylate levels is blended with the higher performance elastomer in the skin layers to act as a compatibilizer and improve adhesion to the core layer and fibrous outer layer in a laminate. The skin layer aids in reducing die lip buildup during the film extrusion process.
In a further aspect of the invention, a styrenic block copolymer elastomeric resin is added to the elastic skin layer(s) to act as a compatibilizer to assist in the adhesion of two incompatible materials, such as those found in the core and skin layers.
In still a further aspect of the invention, the microporous film of the present invention is laminated to a fibrous layer. The fibrous layer can be a nonwoven web such as, for example, an extensible nonwoven web. Film nonwoven laminates of the present invention can be used as a barrier layer in bodily articles such as, for example, in diapers as outer covers, adult incontinence garments, protective apparel and the like. Additionally, and in still a further aspect of the present invention, the breathable microporous films and/or film laminates of the present invention make up a component of an absorbent bodily article. As one example, an absorbent bodily article can include a liquid pervious liner; an absorbent core; and a microporous film or film laminate of the present invention wherein the absorbent core is positioned between the liquid pervious liner and microporous film or film laminate.